JPS59216032A - Measuring device of resolving power of lens - Google Patents

Abstract

PURPOSE:To grasp sensually and extremely clearly resolving power and to evaluate objectively and accurately the resolving power by providing a chart member with a resolving power chart and a slit for MTF measurement. CONSTITUTION:When the chart member 1 is irradiated with incoherent light from an illumination lamp LS, an image Im of the chart member 1 is formed on the photodetection surface of a measuring member 2 through a rotatable lens L to be inspected. At this time, images of resolving power charts C1-C3 of the chart member 1 are projected on the screen 22 of the measuring member 2, so those images are observed visually to evaluate the resolving power of the lens L to be inspected immediately. Images of slits SL1-1-SL3-2, on the other hand, are projected on solid-state image pickup elements S1-S6. The respective solid-state image picture elements S1-S6 scan the projected slit images and their outputs are processed by a Fourier transforming means to calculate MTF, thus evaluating accurately and objectively the resolving power of the lens L to be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an apparatus for measuring the resolution performance of a lens.

(Prior Art) Conventionally, the resolution performance of a lens has been measured by directly visually observing the image of the test lens on a resolving power chart having a group of striations having a plurality of spatial periods. A resolution chart method to judge the resolution performance of
An MTF method is known that measures the MTF of a lens to be tested.

The resolution chart method is simple and allows rapid measurement of resolution performance, but on the other hand, since it is a visual inspection with the naked eye, there are problems such as image error and fatigue of the measurer.

On the other hand, the MTF method allows objective and accurate evaluation of resolution performance.

However, despite the problems mentioned above, the resolution chart method remains popular as a method for measuring resolution performance, and the MTF method has not been commercialized despite its accuracy and objectivity. However, lenses such as FJf are still often avoided.

While the resolution chart method has strong popularity, the MTF' method is avoided for the following reasons.

In other words, the resolving power chart method is simple and simple, as it directly visually observes the image of the lens being tested on the resolving power chart to judge the resolution performance.
The quality of resolution performance, which is the object of measurement, can be grasped very clearly intuitively.

On the other hand, in the MTF method, the target of judgment is the MTF, which is calculated and quantified according to a certain method from the imaging state of the image, and it is a national problem to intuitively understand the weaving performance itself. There is a thing. In addition, so far, evaluation of resolution performance using the resolution chart method and MTF
There is also no thorough analysis of the correspondence between evaluation methods.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lens resolution performance measuring device that can measure the resolution performance of a lens from both the resolution chart method and the MTF method.

(composition) The present invention will be explained below.

A resolution performance measuring device according to the present invention includes a holding means, a rotating means, a chart member, an illumination lamp, and a defining member.

The holding means holds the lens to be tested whose resolution performance is to be measured so as to be rotatable about the optical axis. Here, the optical axis refers to the optical axis of the measuring device itself, and is fixed to the device. The lens to be tested is held by the holding means so that its optical axis coincides with the optical axis. Therefore,
In principle, the above-mentioned optical axis and the lens optical axis of the test lens coincide, but the test lens is generally held by a holding means in a state where it is held in a lens barrel. It should be noted that if the lens optical axis is oriented with respect to the lens barrel, the optical axis and the lens optical axis may not coincide with each other.

The rotating means rotates the lens to be tested around the optical axis as necessary. When rotation is performed by mechanical force, the rotation means is generally composed of a motor as a driving source for rotation and a transmission system that transmits the driving force of the motor to the holding means. Since it is known, all you have to do is select the appropriate one and use it.

The chart member has an elongated flat plate shape, and is fixedly disposed such that its longitudinal center portion coincides with the optical axis of the measuring device and is orthogonal to the optical axis. However, here, "fixed" refers to the state at the time of measurement, and it goes without saying that the positional relationship with the test lens may be adjustable.

One or more resolution charts are arranged on one side in the longitudinal direction of this chart member, and one or more resolution charts are arranged on the other side.
A slot for TF measurement is provided. The one or more resolution charts and the slots are symmetrical with respect to the optical axis.

The Fuming lamp illuminates the chart member with inocoherent light.

The measurement member is arranged at a position conjugate with the chart member with respect to the lens to be tested. Thus, when the illumination lamp illuminates the chart member, an image of the chart member, the resolution chart and the slit is projected onto the measuring member.

The part of the 311.1 constant member on which the image of the above resolution chart is projected is a screen part. Furthermore, a solid-state image pickup device for scanning the slit image is provided at a portion where the slit image is projected.

Hereinafter, specific examples will be described with reference to the drawings.

In FIG. 1, the reference numeral indicates the lens to be tested, the reference numeral 1 indicates the chart member, the reference numeral LS indicates the illumination lamp, the reference symbol B indicates the optical axis, and the reference numeral 1 indicates the group of chart members according to the test lens L. There is.

The lens L to be tested is fixed on a mount (not shown),
It is rotatable. Of course, at this time, the lens optical axis coincides with the optical axis bar.

As shown in FIG. 2, the chart member 1 has an elongated flat plate shape, with its longitudinal center aligned with the optical axis AX,
It is fixedly arranged perpendicular to the optical axis.

In the longitudinal direction σ) of this chart member 1, a light T
', #lI At a distance l+1'2+'3 from the optical axis AX, )1J image cutters 1-C1, C2, C3 are arranged, and on the opposite side, 4.
Three pairs of slots are placed at positions a, , x3.

The pair of slits SLI 1 and SLI 2 is symmetrical to the 'M image chart C1 with respect to the optical axis system. Also, surin l-5L2-1, a pair of 5L2-2, surin) 5L
3-1 and 5L3-2 are symmetrical to the optical axis with C2 and C3, respectively.

Resolution charts) C1, C2, and C3 are the same, and as shown in FIG. 3, they are notated as a group of striations having a plurality of spatial periods.

Slits 5LI-1, 5L2-1, and 8L3-1 are slits for measuring MTF in the radial direction,
SLI 2. SL22. SL32 is a slit for measuring MTF f in the tanogenic direction. In this example, the chart member 1 is formed by polishing the surface of an optical glass plate well and depositing chromium to form a putter 7 with a resolution chart, slits, and grooves.

In FIG. 1, when the chart member is illuminated with incoherent toner light from the illumination lamp LS, an image 1111 of the chart member
The image is formed at a position conjugate to .

Now, as shown in FIG. 4, the 1ll11 fixed member 2 has a screen substrate 21 and 4p formed on one half in the longitudinal direction, and a slide substrate 24 on the other half.

The screen substrate 21 includes a light-transmitting and diffusive screen 2.
2 is provided, the slide substrate 24 has a substrate 231,
232.233. 234.235. 236 are arranged, and a CCD as a solid-state image sensor is arranged on each of these boards. Reference numerals 81 to S6 indicate these CCDs. The light receiving surfaces of the solid-state image sensors S1 to S6 and the screen 21 are on the same plane. Also, the fourth
In the figure, reference numeral 25 indicates a CCD relay board.

The measuring member 2 is arranged so that the image Im shown in FIG. 1 overlaps the light receiving surface.

Then, the resolution chart ()CI in chart member 1
, C2 and C3 are the images of the screen 22 of the measurement member 2.
Since the image is projected upward, the lunar image performance of the lens L to be tested can be immediately evaluated by visually observing this image.

- direction, Sri Soto 5LI-1, 8L
I-2, 5L2-1. 5L2-2゜5L3-1.
The images of 8L3-2 are respectively captured by solid-state image sensors S2.8L3-2.
SL, S4. S3. 86. On top of S5,
The light is projected so as to intersect the light receiving areas of these elements. Each solid-state image sensor S1 to S6 scans the projected slit image,
The output is subjected to predetermined processing such as Fourier transform calculation, and +
vlTF is calculated. MTF obtained in this way
Accordingly, the resolution performance of the lens L to be tested can be evaluated accurately and objectively.

From this state, if the lens L to be tested is rotated 180 degrees around the optical axis, the resolution performance can be measured using the resolving power chart in the lens position where the MTF was previously measured. It is possible to measure the MTF in a state where the resolution performance is evaluated by

Therefore, the resolution performance of the same lens L to be tested can be measured simultaneously from the resolution chart method and the MTF method, which is very useful when analyzing the correspondence between the two measurement methods. Highly accurate measurement becomes possible.

Lenses used in slit exposure type copying machines and lenses used in facsimile reading devices have problems with resolution performance in the longitudinal direction of the slit exposure section or in the direction of the reading line. , and the longitudinal direction of the chart member, it is possible to achieve a desired resolution performance very easily.

In addition, the test lens L is rotated around the optical axis by a predetermined angle, for example, by 0.36 degrees, and measurements are taken at each rotation step. , resolution performance in all directions can be measured. In order to rotate the lens to be tested around the optical axis 9 by a constant angle in this manner, it is preferable to use a stepping motor as the drive motor of the rotation means.

Of course, the rotation of the lens to be tested may be performed manually or may be automatically controlled using a computer or the like.

Further, the resolution chart and the number of slits disposed symmetrically with the optical axis may be appropriately set to a number of 1 to 2 depending on the number of measurement points. Further, the screen portion does not necessarily have to be translucent.

In addition, since the chart member in the measuring device of the present invention is equipped with a resolution chart and a slit, even if the chart member can be miniaturized, there is a limit to the size of the chart member, and the entire device is only 9. If an attempt is made to prevent the image from becoming humanoid, the lenses to be tested will be limited to those that can be used for protection at low magnifications, several times at most. From this point of view, the measuring device of the present invention is most suitable for measuring the resolution performance of low-magnification lenses used in copying machines and facsimile reading devices.

(Effects) As described above, according to the present invention, a novel lens performance measurement device can be provided.

According to this measurement device, the resolution performance of the lens to be tested can be measured from both the resolution chart method and the MTF method, and it is possible to grasp the resolution performance very clearly intuitively, as well as to measure the resolution performance objectively and accurately. can be evaluated.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG.
The figure is a plan view showing a chart member used in the above embodiment;
FIG. 3 is a diagram for explaining a resolution chart, and FIG. 4 is a front view showing a measuring member used in the above embodiment. L...Test lens, 1...Chart member, LS...
・Illumination lamp, ■... Optical axis, C1, C2, C3...
Resolution chart, 2... Measuring member, 22... Screen, Sl, S2゜-, S6... Solid state scanning element (
C'CD), 5LI-1, 8LI-2. ,,,, 5L3-1, 8L3-2-... pickpocket,
1.

Claims (1)

[Claims] Resolution 1] 1? 4111 A holding means for holding a test lens to be determined rotatably around an optical axis, and a test lens held by this holding means are rotated around the optical axis as necessary. a rotating means for moving the device; a rotating means that is in the shape of an elongated flat plate, whose central portion in the longitudinal direction coincides with the optical axis, and is fixedly disposed perpendicular to the optical axis; It has the above resolution chart, and on the other side, MT
A chart member having a slit for F measurement, an illumination lamp for illuminating the cono chart front month, and a screen portion onto which an image of the resolving power chart by the test lens is projected;
and a solid-state image sensor that scans the size of a slit formed by the lens to be tested, and a measuring member disposed at a position conjugate with the chart member with respect to the lens to be tested.
What is the resolution performance of the lens? ltt + fixed device.